Human Factors: The Journal of the Human Factors and Ergonomics Society

With the use of available data, search time and stimulus processing rate for a multidimensional target in an array of such stimuli were analyzed with respect to number of displayed stimuli and total stimulus information. The major findings were that search time decreases and stimulus processing rate increases as the number of dimensions in a multidimensional target increases, and that the rate of processing increases as a function of total stimulus information. A model of total stimulus information which assumes sequential processing of dimensions in order of increasing features or levels was found to fit the data.

A visual search model, VIDEM, has been formulated for predicting the detectability of a single, unknown target in an unstructured surround. The intended application is aircraft detection. The model consists of four components: a liminal contrast threshold, a frequency-of-seeing curve, a soft shell search representation, and discrete cumulation of single glimpse detection probabilities. The formulation was developed by registering five existing models against three controlled search experiments. The five models used represent all appropriate laboratory threshold data, including those of Blackwell, Lamar, Sloan, and Taylor. The search experiments included a large set of aircraft field tests, with precise photometric target measurements correlated to the detection events. The model registrations were done using nonlinear parameter estimation techniques and by comparing model predictions to actual event cumulatives with the Kolmogorov-Smirnov statistic. The resultant VIDEM model is a derivative of Sloan's data, cast into the popular visual lobe equations of Lamar.

Visual search time on color-coded information displays has previously been shown to depend upon the number of items displayed (density), the number of colors used (code size), and the number of items in the same color category as the target. The present paper employed regression analysis techniques to develop models of search time which explain the mode of operation of these factors. The initial model, based upon number of items per category as the effective parameter, was successful in explaining 58% of the variation in search time means. An improved model, which introduced the concept, “operative number of colors,” accounted for 84% of the variation. This model was able to postdict 82% of the actually obtained search time values within 0.76 s, with no postdiction in error by more than 2 s. The elevation in search times with larger display densities and code sizes observed in the data, and described by the improved model, was interpreted in terms of disruption of subjects' scan behavior on the more crowded displays.

In the past, investigations into the effects of target uncertainty on search times have been confined to tasks where the stimulus material is carefully structured. The results have been interpreted in terms of models of pattern recognition. In this paper target uncertainty was studied in tasks where subjects could exert greater freedom in determining their scanning strategies. With eye movement recording, it was established that skewed distributions of search times are obtained even when subjects adopt comparatively systematic strategies. There was no evidence that processing time, as reflected in eye fixation times, was generally lengthened with increase in target uncertainty. The observed effects of target uncertainty were discussed in relation to how subjects attempt to overcome the problem of searching simultaneously for targets of different conspicuity.

Two embedded target visual search displays were used in three kinds of experiment. One display had a color and the other a monochrome texture background. In each trial of each experiment a single target was presented. First, 28 observers rated the discriminability of five color and four monochrome targets from the color and monochrome backgrounds, respectively. Second, five observers searched the color and six the monochrome display for the appropriate targets and, after practice, there were 60 trials per observer per target. Third, using the five observers who searched the color display and four of the six who searched the monochrome, the extent into the periphery that they could see the appropriate targets when the displays were exposed for 0.3 seconds was measured. Analysis of the data showed that, for the color displays, simple equations, developed for competition search situations, could be used to relate together the three types of measure. The equations were less successful for the monochrome display.

Target stimuli (the numeral 5 at 60 degrees to the left of the subject's fixation point) were extinguished at various times during the subject's eye movement to that stimulus and the subject was asked to guess what numeral had occurred. Threshold functions were constructed from these data, and it was found that at the beginning of the backward compensatory movement, very little information was transmitted. However, as the backward compensatory movement progressed, there was an increase in the correct identification of the stimulus, and a threshold was reached before the forward compensatory movement began.

The preprogramming of saccadic eye movements is examined by studying the pattern of oculomotor sequences while scanning a visual display. The effects of interference employing a backward masking paradigm on the oculomotor response as well as on position judgment and stimulus identification are examined. Data indicate that the motor programming of an ocular saccade is linked to the perceptual analysis of target position and cannot be set in motion with an impairment in perceptual localization.

The purpose of this paper is to provide a designer or systems analyst a guide to human performance limitations in vision when fixation must be redirected from one display to another. The focus is on large angular separation (greater than 20 deg) and on tasks wherein speed is of importance. Patterns of eye and head movements are shown, as well as quantitative data on saccades, periods of eyelhead compensation, and head movement. Independent variables include interdisplay angle, display visibility, operator's knowledge of display location, and some relevant characteristics of a possible task which must be interrupted for the refixation. Intersubject and intrasubject variability are also presented.

This report was initiated to review the techniques and modifications developed by the U.S. Army Aeromedical Research Laboratory for assessing visual performance/workload of pilots during helicopter operations. Although the corneal reflection technique for gathering eye movement data is not new, innovative modifications had to be developed to permit accurate data collection in this flight environment. This study reports on these techniques, modifications, and applications.

The emphasis on aviator workload has been of primary concern to the U.S. Army aviation community since the incorporation of low altitude terrain flight techniques into the helicopter tactics repertory. Since navigation is a particularly acute problem at low altitudes, this project examined the visual workload of the navigator/copilot during terrain flight (nap-of-the-earth, contour, and low level) in a UH-1H helicopter. Visual performance was measured via a modified NAC Eye Mark Recorder used in conjunction with a LOCAM high speed camera. This technique provided the means to record objectively and analyze the navigator's visual performance.

A visual free time task was utilized to determine the amount of visual time the navigator had available, during flight over the prescribed course, for a nonflight-related task. The data indicate that the navigator's normal workload was demanding; the visual free time task was utilized only 3% of the total time. The data also indicate that the duty of navigating required 92.2% of the copilot's total visual time, while the engine and flight instruments were utilized only 4% of the time. These data are discussed in relation to the copilot's specified duties.